The present invention relates generally to a zoom lens and an imaging system that incorporates it, and more particularly to a zoom lens well suitable for use with electronic imaging systems such as digital cameras and video cameras, wherein depth size upon received at a collapsible lens mount is reduced by tweaks applied to an optical system portion such as a zoom lens, and an imaging system.
In recent years, digital cameras have attracted attention as next-generation cameras superceding silver-halide 35-mm film cameras. In addition, they are now available in some considerable categories covering every type from the business-application, multifunctional type to the portable low-end type.
In view of the portable, low-end type category in particular, one specific objective of the present invention here is to provide a technology of achieving video cameras and digital cameras that are slimmed down in the depth direction while getting hold of high image quality. The greatest bottleneck to slimming down the depth dimension of a camera is the thickness of an optical system, especially a zoom lens system, from the surface nearest to the object side to the imaging plane. The so-called collapsible lens barrel designed to flip an optical system out from within a camera body upon taking and flip it back in the camera body during taking-along is now in vogue.
Slimming-down and downsizing may be achieved by use of a smaller imaging device. However, its pixel pitch must be smaller so as to maintain the same number of pixels, and poor sensitivity must be compensated for by the optical system. This is also true of the influence of diffraction. Therefore, an optical system having a fast F-number is in need.
Some examples of a prior art relatively compact zoom lens having a fast F-number, a zoom ratio of as high as about 3 and a wide angle of view are shown in patent publications 1, 2, 3, 4 and 5.
In these zoom lenses, however, each of zoom lens-forming lens units has an increased axial thickness, offering a problem that even upon received at a collapsible lens mount, the dimension of the lens barrel in the thickness direction is not fully slimmed down, failing to make an associated camera sufficiently small.
Patent Publication 1
JP(A)2002-277740
Patent Publication 2
JP(A)2003-140041
Patent Publication 3
JP (A) 2004-4765
Patent Publication 4
JP(A)2004-61675
Patent Publication 5
U.S. Pat. No. 6,710,934